This application is a continuation-in-part of the Hoover and Osborne U.S. patent application Ser. No. 07/350,338, entitled STRING VIBRATION SUSTAINING DEVICE, filed on May 12, 1989 which has matured into U.S. Pat. No. 4,941,338.
The present invention relates to an electronic device for use in connection with a musical instrument, and more particularly to an electronic device for sustaining the vibration of a string of a stringed musical instrument.
It has long been known that an amplifier can be coupled to a stringed musical instrument to amplify the sound produced by the vibration of the strings of the instrument. Probably the most popular example of such an electrically amplified stringed musical instrument is an electric guitar. An electric guitar typically includes a plurality of strings that extend between the headstock of the guitar and the body of the guitar. A fretted neck is interposed between the headstock and body of the guitar.
In an electric guitar, one or more magnetic pickups are placed on the body of the guitar in magnetic proximity to the strings of the guitar. The magnetic pickups are responsive to the change in magnetic flux caused by the vibration of the strings. This magnetic energy picked up by the pickup is then transmitted to an external amplifier and speaker.
It has long been known that a pickup and external amplifier arrangement on an electric guitar can not only adjust the volume of the sound produced by the guitar, but can also be used by the musician to alter the nature of the sound produced by the guitar. One means for altering this sound is to introduce vibrational feedback into the system to prolong the vibration of the strings of the guitar.
An early method for producing such sustained vibration was for the musician to move the musical instrument in close proximity to the speaker of the amplifier through which the guitar was being amplified. In such a situation, the acoustic energy caused by the sound waves emanating from the speaker would establish a sympathetic vibration of the strings. The vibration of the strings induced by the speaker would then be translated into magnetic flux energy picked up by the pickup means. This magnetic flux energy would then be transmitted through the external amplifier, and would be transformed into sound energy through the speaker of the amplifier. Typically, this situation would result in a "feedback" loop that sustained the vibration of the strings of a musical instrument, and hence the duration of the sound produced by the plucking of the string.
One difficulty, however, with this method of introducing feedback is that it is often difficult to control the amount and type of feedback produced. Hence, it is difficult to control the sound produced through the use of this feedback system. Several devices have been invented to overcome the problems discussed with the above method of sustaining string vibration.
A typical prior art sustain device 8 is shown in FIG. 1 as including a magnetic pickup 10, a magnetic driver 12, and an amplifier 14 interposed between the pickup 10 and driver 12. The pickup is typically comprised of one or more pickup coils, such as pickup coil 11. The driver 12 is typically comprised of one or more of the driver coils, such as driver coil 13.
The sustain system 8 may be used to sustain the vibration of a single string, such as string 16, or a plurality of strings, such as the 4, 6, or 12 strings typically found on an electric guitar. The sustain system is usually disposed on a counter-sunk portion of the upper surface of the body of the electric guitar, so that the pickup 10 and driver 12 are in magnetic proximity to the string 16 of the instrument.
The pickup 10 and driver 12 are constructed generally similarly. Both the pickup 10 and driver 12 are constructed of a number of turns of a conductor means, such as a wire 18, 20 which is wound around a magnetic core 22, 24, respectively. The cores 22, 24 are generally either a permanent magnet, or a ferrous material in contact with a permanent magnet, to provide a permanent magnetic flux through the center of the respective pickup coil 11 and driver coil 13.
The output signal from the pickup 10 is fed to an external amplifier 25. The amplifier 25 amplifies the signal, and feeds the signal to a transducer such as loudspeaker 27. Loudspeaker 27 converts the signal into sound energy which can be heard by the user.
For purposes of this discussion relating to the manner in which such a sustain system works, the pickup coil 11 and driver coil 13 are modeled as ideal inductors, L.sub.P and L.sub.D, respectively, having N.sub.P and N.sub.D, respectively, turns of wire. The amplifier 14 is modeled as having infinite input impedance, zero output impedance, and a voltage gain of A. The string 16 is assumed to be under tension, free to vibrate, and secured at both ends.
A number of sustain systems exist currently. Among those sustain systems known to Applicants are the SUSTAINIAC Model B sustain system, manufactured by Maniac Music, Inc., of Indianapolis, Ind. This SUSTAINIAC sustain system is described in the Applicant's U.S. patent application Ser. No. 06/937,871, which was filed on Dec. 4, 1986.
Another example of a sustain system is the commercially available E-BOW sustain system manufactured by Gregory A. Heat of Los Angeles, Calif., and described in U.S. Pat. No. 4,075,921; and the sustain system described in Holland U.S. Pat. No. 4,236,433.
Notwithstanding the existence of the above mentioned sustain systems and others, room for improvement exists in the manufacture and design of sustain systems. This room for improvement exists to overcome various problems and difficulties associated with sustain systems.
One difficulty associated with a sustain system is the difficulty of using the driver as a pickup during such times as the driver is not being used as a driver. As the driver is not normally used as a pickup to produce an output in response to string vibration, the driver is generally constructed to have fewer turns of wire (N.sub.D) around its core than the pickup (N.sub.P). The fewer number of turns of wire around the driver (relative to the pickup) lowers the voltage drive requirement, and therefore the cost and complexity of the amplifier, that provides the drive current to the driver. However, the fewer turns of wire of the driver produce a lower output voltage in response to string vibration when the driver is being used as a pickup. Due to this lower output voltage, the signal produced by the driver, when the driver is being used as a pickup, does not match well with the signal produced by the pickup.
As will be appreciated, it is desirable to use the driver as a secondary pickup to avoid the need for an additional secondary pickup in addition to the primary pickup. For example, many guitars currently use multiple pickups. This use of multiple pickups limits the space available in which to place a driver. Further, the addition of a driver can detract from the cosmetic appearance of the guitar. Thus, it is desirable to provide a driver which can serve "double duty" as both a driver and a pickup to overcome these problems of spatial constraints and adverse cosmetic impact.
Another problem caused by the inability of current drivers to function as pickups relates to the permanent magnetic field created by the driver. Even when the driver is turned "off" and not being used to sustain string vibration, a magnetic field from the driver can still be "sensed" by the strings and causes a vibration damping effect on the strings. This vibration damping effect of the driver can reduce the natural vibration of the string. If the driver can serve as both a pickup and a driver, a guitar can be manufactured having one less pickup, thus reducing the vibration-depleting magnetic field produced by the pickups and driver.
As will also be appreciated, the ability of a driver to serve both as a pickup and a driver can reduce the cost of manufacturing a guitar, as the ability of the driver to do "double duty" eliminates the need for an additional pickup.
Another problem with known sustain devices relates to the interference caused by load generating devices. Load generating devices include such things as volume controls, tone controls, and transmission cables.
These load generating devices can affect the output signal produced by the pickup. This impact on the output signal affects not only the signal transmitted to an external amplifier and speaker, but can also affect the output signal from the pickup that is transmitted to the driver. Thus, the load generating device can impair the performance of the sustain device.
Another problem associated with known sustain systems relates to the efficiency of the driver. Because of the inductive reactance of a driver, it has been found by the Applicants that the driver may be inefficient at transmitting magnetic energy of certain frequencies to a string. This lack of efficiency appears most pronounced at relatively higher frequencies. The result of this inefficiency is that it tends to narrow the effective band width of string harmonics capable of being induced and sustained by the driver.
An additional side effect of the use of an inefficient driver is the relatively large power consumption of an inefficient driver. This large power consumption is especially undesirable in battery powered sustain systems. By making the driver more efficient, power consumption can be decreased while the level of sustain is maintained.
A further problem associated with some known sustain systems relates to the adverse impact on a driver caused by misalignment of strings during manufacturing of the instrument and string bending techniques performed by the musician. Typically, prior art drivers have consisted of a permanent magnet core having a set of magnetic pole pieces (e.g. 6 for a 6 string guitar). The permanent magnet core is disposed in a coiling of wire. The pole pieces were generally constructed of a ferrous material, and placed in contact with the permanent magnet core to give the pole pieces a permanent magnetic flux. An example of such a pole piece is seen on the well known Humbucking pickup disclosed in Cohen U.S. Pat. No. 3,742,113. Alternately, pole pieces in pickups have been constructed of permanent magnets. Such an arrangement is shown in single coil pickups produced by the Fender Guitar Company of 1130 Columbia Street, Brea, Calif. 92621.
The individual pole pieces of prior art pickups are arranged under each string, so that each string has its own individual pickup coil. In some cases, the poles are adjustable in a vertical plane to enable the user to adjust the pole pieces to a position relatively closer to, or relatively farther away from, the string. This adjustment allows the relative volume of each string to be adjusted independently.
One difficulty with such individual pole pieces is that string bending or misalignment of the strings relative to the pole piece adversely affects the pickup's output in response to the string vibrations. In either case, the string moves away from the pole piece, thus reducing the output of the pickup.
To overcome these problems, it has been found that a pickup having a single pole piece oriented generally perpendicular to the strings allows for a constant output, regardless of string bending or misalignment. This style of pickup is shown in the KPU-13 style pickups produced by Kamen Music Corporation of Bloomfield, Conn. Additionally, a sustainer produced by Kramer Music Products, 685 Neptune Boulevard, Neptune, N.J. 07753 exists that includes a dual coil driver wherein one of the driver coils has a single pole piece, and the other driver coil has individual pole pieces. To date, however, no known drivers have been produced that use a curved driver pole piece to maintain a constant distance from the strings.
As can be appreciated from the above recitation of problems, room for improvement exists in sustain systems. It is, therefore, one object of the present invention to provide a sustain device that improves over prior sustain devices by solving one or more of the problems discussed above.